The invention relates to a home device (domestic appliance) for drying laundry, comprising a component around which process air can flow, said component having a metal substrate which has a surface facing the process air.
A domestic appliance of this kind, embodied as a tumble dryer for drying laundry, is disclosed by each of patent documents WO 2007/093461 A1, WO 2007/093467 A1 and WO 2007/093468 A1. The appliance is embodied in each case as a tumble dryer for drying damp laundry. It comprises a drying chamber embodied as a rotating drum for accommodating the damp laundry and a process air circuit in which the drying chamber is incorporated and in which a stream of process air circulates. Before entering the drying chamber, the process air is heated by a heat source so that it can absorb moisture from the laundry items being tumbled in the drying chamber. After passing through the drying chamber, the moisture-laden process air is first fed to a fluff filter which collects most of the fine particulate fibers entrained by the process air from the laundry. It then passes to a heat sink where it is cooled. During said cooling, the moisture dissipated by the process air is precipitated from process air as a condensate. The condensate is separated from the process air and stored for subsequent disposal. From the heat sink, the process air is returned to the heat source where it is re-heated and fed back to the drying chamber. Even though the fluff filter catches and retains most of the fluff, the heat sink is significantly contaminated by ultrafine fibers which the fluff filter cannot intercept. The problem is exacerbated in that the fluff is deposited on the heat sink surface facing the process air and adheres thereto to a greater or lesser extent, an effect to which the liquid condensate which collects in the heat sink significantly contributes.
A component for a domestic appliance in the form of an air-to-air heat exchanger emerges from DE 20 2004 007 070 U1. Said heat exchanger consists of tubes made of a plastic material such as polypropylene through which process air contaminated with fluff and moisture is designed to flow. The correspondingly exposed insides of the tubes can be provided with an anti-adhesive or hydrophobic microstructure or coating so that they are less prone to fouling.
If the heat sink is embodied as an air-to-air heat exchanger wherein a flow of cooling air drawn from the appliance environment and returned thereto is guided in an open duct and absorbs the heat from the process air, the air-to-air heat exchanger is generally embodied such that, on completion of a drying process, or after a certain number of drying processes in each case, it can be easily removed from the domestic appliance without using a special tool and cleaned simply by rinsing with water. However, if the heat sink is part of a heat pump in which the heat removed from the process air in the heat sink is pumped to the heat source where it is returned to the process air, it is generally no longer possible to embody the heat sink such that it can be readily removed by an ordinary user. The compressor-type heat pump mentioned in the three documents referred to above connects the heat sink and the heat source in a heat transfer circuit in which a working medium circulates, said working medium being in particular a fluorinated hydrocarbon. The latter flows to the heat sink in liquid form where it is evaporated, for which purpose it absorbs heat from the process air. It is fed in evaporated form to a compressor where it is compressed and conveyed forward to the heat source. Here it is liquefied by discharging heat to the process air. Downstream of the heat source, the working medium is fed to a restrictor which can be a valve, an orifice plate or a capillary, where its internal pressure and its temperature are reduced, and from there back to the heat sink, thereby completing the circuit. In order to ensure long-term operation of this circuit, it must be virtually completely sealed. Conventional practice is to interconnect all the components of this circuit by soldering. This makes it impossible for an ordinary user of the domestic appliance to detach the heat sink from this circuit, as would be required for removing the heat sink from the appliance. The same applies if the heat pump is a thermoelectric heat pump. A thermoelectric heat pump which uses the well-known Peltier effect is according to normal practice a compact unit consisting of two heat exchangers, namely the heat sink and the heat source, between which are mounted the so-called Peltier elements in which the Peltier effect used for pumping the heat is produced by electric current. It is also impossible to remove the heat sink in this heat pump. If in the case of a domestic appliance having a heat pump it is therefore desired to de-fluff the heat sink, other means have to be provided. The three documents mentioned indicate the possibilities of cleaning the heat sink by means of brushes and using additional liquid.
The invention relates not only to domestic appliances for drying laundry in the form of the tumble dryer described, but also to domestic appliances in which laundry can be both washed and dried. Such appliances are known as “combo washer/dryers”. It is irrelevant whether or not the heat sink present in such an appliance is a component of a heat pump.
DE 103 30 744 A1 discloses a coating system based on hydrolyzable silanes with high hydrolysis rates. This coating system is designed to lend itself to producing functional coatings having different properties, particularly the property of being easily cleanable, and also to be highly scratch-resistant and suitable for substrates made of glass, ceramic, metal, stone or plastic. A coating produced using a coating system of this kind is based on a so-called polysiloxane resin. A coating system described in the publication cited as “Example 2” is suitable for producing a hydrophobic easy-to-clean coating with very low surface energy, which means that dirt and liquids can stick only very weakly to the coating. As a result the coated surface is not heavily prone to fouling and is easy to clean. However, the lasting adhesion and durability of this coating requires heat treatment at a temperature above 200° C., which limits the applicability of the coating only to correspondingly stressable substrates, in particular metal substrates.
Further examples of easy-to-clean coatings are disclosed in document WO 2001/064 801 A1 which likewise shows coating systems based on polysiloxane resins. In this respect attention should be drawn in particular to the exemplary embodiments designated “Example 2B”, “Example 9”, “Example 34”, “Example 39” and “Example 40”. In each case a coating is produced which makes the surface dirt-repellent, which is scratch-resistant and in some cases also capable of withstanding high temperatures. Typical applications in or on a private household are protecting walls from graffiti and also the protective, corrosion-resistant and non-stick coating of cookware, stoves and other equipment.
An object of the present invention is to develop the domestic appliance of the generic type cited in the introduction such that an improvement is achieved in respect of the removal of fluff and other foreign particles from a component, in particular a heat sink, around which process air can flow.